Electrostatic coating system

ABSTRACT

An electrostatic coating system characterized by a chamber containing a level of fluidized powder, an adjustable electrode for controlling the coating thickness on the part being coated and overflow weirs for controlling the level of fluidized powder with respect to such part.

United States Patent Inventor Robert L. Koch, ll

' Evansville, Ind.

Appl. No. 769,913

Filed Oct. 23, 1968 Patented Aug. 17, 1971 Assignee Ashglee Evansville, Ind.

ELECTROSTATIC COATING SYSTEM 3 Claims, 3 Drawing Figs.

U.S. 1 18/629, 1l8/DlG.5,118/6 34,117/17,1l7/D1G.6 Internationalclassification B05c 5/02 Field ofSearch 117/17; 118/629, 634, 304, 312, 400.5,,404, 405

References Cited UNlTED STATES PATENTS 2/1952 Harms 117/F.B. 4/1966 Barford et al.. 118/629 X 8/1967 Point 117/17 X 8/1968 Beebe et al.... 118/634 9/1968 Tauveron ll7/F.B.

Primary Examiner Peter Feldman AttorneyWarren D. Flackbert ABSTRACT: An electrostatic coating system characterized by a chamber containing a level of fluidized powder, an adjustable electrode for controlling the coating thickness on the part being coated and overflow weirs for controlling the level of fluidized powder with respect to such part.

PATENTEU Ans-man 3.599.603

SHEET 2 or 2 4. INVENTOR Rose-er 1Q Wac/I, .3

ATTORNEY ELECTROSTATICCOATING SYSTEM As is known, the use of electrostatic charged powder to coat parts'is'widespread. One approach is the use of an electrostatic gun, either movable by'the operator or mounted in a fixedposition in a spray booth or spray area. Another approach is the use of a porous bed holding a supply of resin powder, where a fluid, such as air, forces the powder through an electrode-where it is charged, and then into contact with the part which is to be coated. In this connection, and by way of example, the part may be a metal pipe which is rotated, through conventional techniques, during the coating opera- 011'. I'

In any event, and considering the fluidized bed approach, previous systems were objectionable insofar as the control of coating thickness was concerned. The latter is also responsive to the powder level and its distance from the part being coated. The invention is highly advantageous in providing features for achieving optimum coating results. In this connection, the electrode, disposed within the resin, is movable vertically to effectively control coating thickness. Moreover, in order to further achieve the same quality of coating, the level of resin powder is maintained constant with respect to the part being-coated through the use of weirs,the latter permitting excess resin powder to be returned for subsequent use.

A better understanding of the present invention will become more apparent from the following description, taken in conjunction with the accompanying drawings wherein:

. FIG. 1 is a view in elevation, partly in'vertical section, showing the'fluidized bed of the invention;

FIG. 2 is a fragmentary view of one approach for positioning the electrode; and,

FIG; 3 is a view in elevation of the overall system, parts of which are represented diagrammatically for clarity in presentation. v

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring now to the figures, the invention is typically shown in conjunction with an arrangement for coating metal pipe 10, the latter passing through a housing defined by a chamber 12 having sliding doors 12a and 12b mounted between brackets 120. Each door has an opening for the pipe 10, and, as necessary,-.may be removed and substituted by another door to accommodate a different diameter pipe 10. Chamber 12 is electrically nonconductive, being made from plastic, for example, and lies over a bed 14 disposed within a base 17 of the housing.

Bed 14 is supported along all edges by walls 15, which also serve as weirs, and walls 17a within and of the base 17 beneath chamber 12,;typically on angle members 16. The bed 14 and anglemembers 16 define an arrangement minimizing air or fluid loss around the edges of the bed 14, where the latter is made from a porous material, such as a type of canvas, for ex ample.

A resin powder 19 is supplied to the bed 14 through feed conduit 20, such resin powder 19 being applied to the parts to be coated. An important feature of the invention is the provision of openings 22 along two opposite sides of the bed 14, ad-

jacent walls or weirs 15, to maintain a constant level of resin powder 19 on bed 14, where it should be understood that the level of the powder 19 with respect to the part 10 is critical. Excess powder 19 passing through the openings 22 is recirculated, through conduit 24, for subsequent use.

An electrode 25, typically a mesh screen having one-quarter inch openings, is preferably positioned within the layer of powder 19 to' directly charge such powder 19, or, alternatively, may charge the air above the powder 19. The electrode 25 is movable throughout the layer of powder 19, i.e., from the top of such powder layer to the bed 14, and although not as effective, may be positioned above the powder level, as well. Various approaches can be provided for the electrode movement, and a typical arrangement is shown in the drawings.

In this connection, nonconductive handles 25a are secured to the electrode 25, a portion 25b of each of which extends through a vertical slot or opening 27 in the walls of base 17. As evident in FIG. 2, one edge 27a of each slot is cut so that the portion 25b of each handle may be received at different heights, selectively positioning electrode 25 with respect to the bed 14.

The system further includes a fitting 30 which receives a conduit (not shown) through which pressurized fluid, such as air, for example, is introduced into the space within the base 17 beneath the bed 14. In other words, and in use, the pressurized fluid moves upwardly through the bed 14, forcing the resin powder 19 which is charged by the electrode 25 upwardly into coating contact with the rotating pipe 10. It should be understood that provisions may be made for vibrating the bed 14, "as through the use of a conventional vibrating mechanism 32 disposed beneath the bed 14 in the region of the angle members 16 (see FIG. 1).

With reference to FIG. 3, conduit 24 passes to structure including a conventional feeding mechanism 34 which includes a mesh screen and a rotary valve (both not shown) for feeding powder to conduit 20 and onto the bed 14. The proceeding may also include a collection bulb 36 for large powder particles unable to pass through the aforesaid screen in the feeding mechanism 34. A dust collector 37, also conventional in form, is disposed above the feeding mechanism 34. Additionally, a fresh powder supply 39 forms a part of the overall system, the latter selectively feeding fresh powder into the feeding mechanism 34 upon demand. Moreover, means may be provided for the removal of tramp iron and agglomerated powder particles.

lmportantly, and as stated above, the electrode 25 controls the coating thickness on pipe 10. The weirs l5 and defined openings 22 serve to maintain a constant distance between the pipe 10 and the top of the powder, again resulting in optimum coating action. The electrode 25, in the form of a screen, in contrast to a pointed electrode which is grounded, is much superior in creating a uniform electrostatic field. The operator can readily move the electrode 25 upwardly or downwardly to control coating thickness, and for optimum results, the electrode 25 is disposed within the powder.

The invention is susceptible to various changes; including proportioning or the like, and therefore, is adaptable for use in various types of installations.

Iclaim:

1. An electrostatic coating system comprising a housing, a

fluidized bed disposed within'said housing, coating material received on said bed, and an electrode positioned in charging relationship with said coating material, said electrode being in the form of a screen member with means for adjusting said screen member upwardly and downwardly to control coating thickness.

2. The electrostatic coating system of claim 1 where said housing includes a weir for maintaining a constant amount of said coating material on said fluidized bed.

3. The electrostatic coating system of claim 1 where said housing is defined by a chamber through which the part being coated passes and a base, and where said chamber is made from an electrically nonconductive material. 

2. The electrostatic coating system of claim 1 where said housing includes a weir for maintaining a constant amount of said coating material on said fluidized bed.
 3. The electrostatic coating system of claim 1 where said housing is defined by a chamber through which the part being coated passes and a base, and where said chamber is made from an electrically nonconductive material. 